The Remote Sensing of Tropospheric Gases by Thermal Emission Spectroscopy

Abstract

A technique for the remote sensing of tropospheric gases for air pollution and global warming has been developed. Models of global warming depend on the measured laboratory absorption spectra of Radiatively Active Gases, yet the atmosphere works on the radiative transfer of thermal emission. An outstanding question is then: are there discrepancies between calculations of radiation codes and atmospheric fluxes? Models of the global warming use laboratory absorption spectra of gases as a basis for radiative transfer calculations. In the atmosphere, the greenhouse effect actually arises through the emission of Planck blackbody radiation from atmospheric gases and aerosols. The measurement of atmospheric gases by thermal emission spectroscopy with FTIR technology is described using a technique which has recently been developed for measuring the thermal emission spectra of gases in a infrared cell in the laboratory. In particular, CFC11, CFC12, HNO3, NO2, SO2, CH4, CH4,C4H10 and N2O5 have been measured in the laboratory. These gases are of importance for investigations of the tropospheric chemistry of air pollution and global warming. The gases measured in the atmosphere include CFC11, CFC12, CFC22, ethylene and nitric acid. As an example, the thermal emission spectrum of CFC11 has been measured in detail. This is compared with the measured laboratory absorption spectrum and with the spectrum of CFC11 from an atmospheric observation. Atmospheric spectra indicating the presence of the several gases have been measured. It is shown that absorption spectra of these gases may not be adequate for detailed radiative transfer calculations in greenhouse models and for satellite thermal emission analysis.